A description of which data are stored on a compact disk and how they are processed by the CD player is presented in the article "Zusammenstellen eines CD-Programms" ("Assembling a CD Program") in "Funkschau" No. 15, Jul. 18, 1986, pp 26 through 28.
Every CD contains a directory which stores data about the number of program blocks on the disk, their start times, as well as the total playback time of the disk. The individual program blocks are normally musical items but they can be, for example, in the form of spoken words or various sound effects for dubbing flims or slides. Up to 99 program blocks can be stored on one CD, but a music CD normally only has 10 to 20 different musical items.
The CD directory has the data format illustrated in FIG. 1. The first block A0 stores the title of the first muscial item, the second block A1 stores the title of the final musical item, and the third block A2 stores the total playback time of the CD. The start times of the individual n musical items, which are stored on the disk, are stored in the subsequent data blocks D1 through Dn. In order to achieve redundancy, several identical blocks are provided. In the example shown in FIG. 1, three identical blocks are arranged in succession on the data track for each function stored. Three blocks A0 are followed by three blocks A1, three blocks A2, three blocks D1, three blocks D2, and so on until, finally, the last three blocks Dn form the end of the directory. After inserting a CD into a CD player, the CD's directory is read. The data present in the directory are stored in a memory of the CD player. Only after all the necessary directory data has been read and stored can the CD player begin to play back the individual musical items. Therefore, after having inserted a CD into a CD player for the purpose of playback, the CD listener must wait until the CD player has read the directory and stored the data. The time required by the CD player to do this, usefully called the read-in time, is an important feature in terms of the quality of a CD player.